1. Field of the Invention
In one of its aspects, the present invention relates to a cleaning formulation for, inter alia, optical surfaces. In another of its aspects, the present invention relates to method for removing fouling materials, inter alia, from an optical surface.
2. Description of the Prior Art
Fluid treatment systems are known generally in the art.
For example, U.S. Pat. Nos. 4,482,809, 4,872,980 and 5,006,244 (all in the name of Maarschalkerweerd and all assigned to the assignee of the present invention and hereinafter referred to as the Maarschalkerweerd #1 Patents) all describe gravity fed fluid treatment systems which employ ultraviolet (UV) radiation.
Such systems include an array of UV lamp frames which include several UV lamps each of which are mounted within sleeves which extend between and are supported by a pair of legs which are attached to a cross-piece. The so-supported sleeves (containing the UV lamps) are immersed into a fluid to be treated, which is then irradiated as required. The amount of radiation to which the fluid is exposed is determined by factors such as: the proximity of the fluid to the lamps, the output wattage of the lamps, the fluid""s flow rate past the lamps, the UV transmission (UVT) of the water or wastewater, the percent transmittance (%T) of the sleeves and the like. Typically, one or more UV sensors may be employed to monitor the UV output of the lamps and the fluid level is typically controlled, to some extent, downstream of the treatment device by means of level gates or the like.
However, disadvantages exist with the above-described systems. Depending upon the quality of the fluid which is being treated, the sleeves surrounding the UV lamps periodically become fouled with foreign materials, inhibiting their ability to transmit UV radiation to the fluid. For a given installation, the occurrence of such fouling may be determined from historical operating data or by measurements from the UV sensors. Once, or before fouling occurs, the sleeves must be cleaned to remove the fouling materials and optimize system performance.
If the UV lamp modules are employed in an open, channel-like system (e.g., such as the one described and illustrated in Maarschalkerweerd #1 Patents), one or more of the modules may be removed while the system continues to operate, and the removed frames may be immersed in a bath of suitable cleaning solution (e.g., a mild acid) which may be air-agitated to remove fouling materials. Of course, this necessitates the provision of surplus or redundant sources of UV radiation (usually by including extra UV lamp modules) to ensure adequate irradiation of the fluid being treated while one or more of the frames has been removed for cleaning. This required surplus UV capacity adds to the capital expense of installing the treatment system. Further, a cleaning vessel for receiving the UV lamp modules must also be provided and maintained. Depending on the number of modules which must be serviced for cleaning at one time and the frequency at which they require cleaning, this can also significantly add to the expense of operating and maintaining the treatment system. Furthermore, this cleaning regimen necessitates relatively high labour costs to attend to the required removal/re-installation of modules and removal/re-filling of cleaning solution in the cleaning vessel. Still further, such handling of the modules results in an increased risk of damage to or breakage of the lamps in the module.
If the frames are in a closed system (e.g., such as the treatment chamber described in U.S. Pat. No. 5,504,335 (in the name of Maarschalkerweerd and assigned to the assignee of the present invention) removal of the frames from the fluid for cleaning is usually impractical. In this case, the sleeves must be cleaned by suspending treatment of the fluid, shutting inlet and outlet valves to the treatment enclosure and filling the entire treatment enclosure with the cleaning solution and air-agitating the fluid to remove the fouling materials. Cleaning such closed systems suffers from the disadvantages that the treatment system must be stopped while cleaning proceeds and that a large quantity of cleaning solution must be employed to fill the treatment enclosure. An additional problem exists in that handling large quantities of cleaning fluid is hazardous and disposing of large quantities of used cleaning fluid is difficult and/or expensive. Of course open flow systems suffer from these two problems, albeit to a lesser degree.
Indeed, once installed, one of the largest maintenance costs associated with prior art fluid treatment systems is often the cost of cleaning the sleeves about the radiation sources. U.S. Pat. Nos. 5,418,370, 5,539,210 and 5,590,390 (all in the name of Maarschalkerweerd and all assigned to the assignee of the present invention and hereinafter referred to as the Maarschalkerweerd #2 Patents) all describe an improved cleaning system, particularly advantageous for use in gravity fed fluid treatment systems which employ UV radiation. Generally, the cleaning system comprises a cleaning sleeve engaging a portion of the exterior of a radiation source assembly including a radiation source (e.g., a UV lamp). The cleaning sleeve is movable between: (i) a retracted position wherein a first portion of radiation source assembly is exposed to a flow of fluid to be treated, and (ii) an extended position wherein the first portion of the radiation source assembly is completely or partially covered by the cleaning sleeve. The cleaning sleeve includes a chamber in contact with the first portion of the radiation source assembly. The chamber is supplied with a cleaning solution suitable for removing undesired materials from the first portion of the radiation source assembly.
In International publication number WO 00/26144 [Pearcey et al. (Pearcey)], published May 11, 2000, there is disclosed a cleaning apparatus for a radiation source module and a radiation source module incorporated such cleaning apparatus. Generally, the cleaning apparatus and related module comprise: (i) a slidable member magnetically coupled to a cleaning sleeve, the slidable member being disposed on and slidable with respect to a rodless cylinder; and (ii) motive means to translate the slidable member along the rodless cylinder whereby the cleaning sleeve is translated over the exterior of the radiation source assembly.
Further improvements to cleaning devices are described in:
copending U.S. patent application Ser. No. 09/258,142 [Traubenberg et al. (Traubenberg)], filed on Feb. 26, 1999;
copending U.S. patent application Ser. No. 60/136,766 [Dall""Armi et al. (Dall""Armi)], filed on May 28, 1999; and
copending U.S. patent application Ser. No. 60/148,648 [Fang et al.(Fang)], filed on Aug. 13, 1999;
each assigned to the assignee of the present invention.
The teachings of Pearcey, Traubenberg, Dall""Armi and Fang each represent important advances in the art, particularly when implemented in a fluid treatment module such as the one illustrated in the Maarschalkerweerd #1 Patents.
One area in the prior art which has received relatively little attention is the nature of the cleaning formulation used in such cleaning devices for optical radiation devices such as the ones taught in the Maarschalkerweerd #2 Patents and in Pearcey, Traubenberg, Dall""Armi and Fang.
It is known that the disinfection efficiency of a UV lamp is dependent on the cleanliness of the surface which houses the UV lampxe2x80x94see Kreft, P.; Scheible, O.K.; Venosa, A. xe2x80x9cHYDRAULIC STUDIES AND CLEANING EVALUATIONS OF ULTRAVIOLET DISINFECTION UNITSxe2x80x9d, Journal WPCF, Volume 58, Number 12, p.1129 [Kreft]. Cleaning of a ultraviolet disinfection system is important in order for the system to operate at optimum efficiency. Surface fouling can significantly affect the dose efficiency needed for meeting the disinfection requirements. Fused quartz sleeves, which are conventionally used to house the radiation lamps, are rated at an ultraviolet transmittance (UVT) of 80 to 90% when brand new. Maintaining the %UVT at or very close to 80% is highly desirable to sustain the ability to meet disinfection requirements.
Fouling on an ultraviolet radiation surface (e.g., the quartz sleeve surrounding the lamp) is complex and can vary from site to site. The three main contributors to fouling include inorganic deposits, organic fouling and biofilms (which can grow when the surfaces are fouled and not fully irradiated)xe2x80x94see Kreft.
The major fouling components of inorganic scale deposits typically comprise one or more of magnesium hydroxide, iron hydroxide, calcium hydroxides, magnesium carbonate, calcium carbonate, magnesium phosphate and calcium phosphate. These are salts with inverse solubility characteristicsxe2x80x94i.e., the solubility of salt decreases with increasing temperature. It has been indicated that quartz sleeves used in ultraviolet radiation systems such as the ones described above will have a higher temperature at the quartz/water interface than that of the bulk solutionxe2x80x94see Kreft. This has led to the suggestion that fouling of such quartz sleeves may arise from the inverse solubility characteristics of the inorganic salts. Other factors such as surface photochemical effects may also lead to fouling.
A conventional method for cleaning inorganic fouled surfaces uses acidic materials. It should be noted that basic chemicals such as ammonium hydroxide or sodium hydroxide are usually avoided due to their chemical interaction with quartz and their limited cleaning efficacy of inorganic debris.
The magnitude of the cleaning ability of acids on inorganic media (inorganic fouling generally consists of metal oxides and carbonates on the quartz or other surface) is related primarily to pH. At low pH, metal cations aquate more easily and, in the important case of fouling by carbonate anions, decomposition via CO2 formation occurs. Acids further have the ability to disrupt ion bridging effects that give rise to fouling films like soap scum and also to solubilize precipitated fatty acid soaps. Most cleaning formulations use very strong acids to remove inorganic water spots, stains and encrustations on surfaces. The cleaning of inorganic substrates is most effectively accomplished by acid treatment when coupled with surfactants that can remove adsorbed organic/inorganic complexes (McCoy, J. W. xe2x80x9cIndustrial Chemical Cleaningxe2x80x9d Chapter 2, pp.34. Chemical Publishing Co. New York, N.Y.).
Acids have the ability to disrupt the ion bridging effects which give rise to fouling films like soap scum and also to solubilize precipitated fatty acid soaps. Most cleaning formulations to date use strong acids to remove inorganic water spots, stains and encrustations on surfaces. Cleaning of inorganic fouling materials has been accomplished by acid treatment which, when coupled with surfactants, can remove adsorbed organic/inorganic complexes.
Wastewater treated by conventional ultraviolet radiation systems may also contain a wide variety of living organisms and organic-based molecules which range from those which are surface active to oils and greases. Surface active molecules, such as humic acids, which are negatively charged can bind polyvalent ions (calcium, iron, magnesium) contained in the water. Additionally, because the surface active molecules contain hydrophobic moieties the adhesion of ultraviolet radiation adsorbing species such as proteins or aromatics can also cause the transmission of the ultraviolet from the lamps to be reduced.
A number of chemicals have been suggested and used for cleaning scale deposits from surfaces with or without organic fouling materials. Inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and sulfamic acid are commonly used in the chemical cleaning of inorganic scale depositsxe2x80x94see Kreft. However all of these acids are corrosive and difficult to handle. Thus, an occupational health concern arises in using such acids. Also, there is an increased likelihood of wear and tear on equipment as a consequence of using such acids. Hydrochloric acid and sulfuric acid typically are not recommended in applications where exposure to stainless steel can occur due to their corrosive action. Nitric acid has oxidation capabilities and can only be used in a concentration of up to about 10% due to its potential reactivity. Phosphoric acid is a relatively safe and efficient cleaning acid, and has been used in a wide variety of industries. However, the use of phosphoric acid may contribute to the formation of insoluble phosphates with iron, calcium or magnesium. Additionally phosphate is a limiting nutrient for microbial and algae growth hence disposal of the cleaning solution and leakage into the treated water needs careful monitoring.
A novel cleaning formulation copending U.S. patent application Ser. No. 60/207,187 [Ketelson et al. (Ketelson)], filed on May 26, 2000. The cleaning formulation taught by Ketelson represents a significant improvement in the art. Specifically, the formulation taught by Ketelson has one or more of the following attributes:
(i) it can remove foreign deposits of organic, biological and inorganic origin from optical and/or metal surfaces;
(ii) it does not chemically interact substantially with the optical surface or leave residual adsorbed species which will substantially reduce the % UVT;
(iii) it is relatively safe to handle and is relatively non-corrosive to human skin;
(iv) it meets the current standards for governing environmentally acceptable usefulness in the wastewater and potable water industries;
(v) it maintains its cleaning activity over time (e.g., months) while being exposed to ultraviolet radiation;
(vi) it possesses anti-microbial properties;
(vii) it is substantially compatible with one or more other ingredients known in the art of cleaning formulations, including surfactants, wetting agents, thickeners, sequestrants and chelating agents;
(viii) it is substantially compatible for use in a wiper compartment and neither substantially degrades the seal material nor substantially retards wiper movement across a surface;
(ix) it is substantially useful in combination with thickeners that exhibit shear thinning properties in order to maintain control over its flow properties;
(x) it meets FDA guidelines for excipients or additives in food or drugs; and
(xi) it is not substantially corrosive toward stainless steel.
Despite the advance in the art provided by Ketelson, there is room for improvement. Specifically, when liquid cleaning formulations, such as the one taught by Ketelson, are used in cleaning systems such as the one taught in the Maarschalkerweerd #2 Patents, there is a likelihood that the liquid cleaning formulation will leak out of the cleaning chamber over time. This is disadvantageous when the fluid treatment system in question is used in a clean (i.e., drinking) water application. Further, this is disadvantageous in that increased costs of cleaning formulations are incurred.
In light of this, it would be desirable to have an improved cleaning formulation which combined the benefits of the cleaning formulation taught by Ketelson while obviating or mitigating the leakage and/or cost problems referred to in the previous paragraph.
It is an object of the present invention to provide a novel cleaning formulation which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art.
It is another object of the present invention to provide a novel method for removing fouling materials from an optical surface.
Accordingly, in one of its aspects, the present invention provides a cleaning formulation comprising a cleaning agent, a particulate clay material and an aqueous carrier, the formulation having a pH less than about 4.0 and characterized by at least a 90% reduction in viscosity at 25xc2x0 C. at a shear rate of up to about 0.10 sxe2x88x921.
In another of its aspects, the present invention provides a method for removing fouling materials from a surface comprising the step of application to the surface a formulation comprising a cleaning agent, a particulate clay material and an aqueous carrier, the formulation having a pH less than about 4.0 and characterized by at least a 90% reduction in viscosity at 25xc2x0 C. at a shear rate of up to about 0.10 sxe2x88x921.
Thus, the present inventor has surprisingly and unexpectedly discovered an acidic (i.e., pH less than 4) cleaning formulation which is thixotropic (also referred to herein as xe2x80x9cshear thinningxe2x80x9d) and has a highly desirable combination of acid stability, temperature stability, electrolyte stability and ultraviolet radiation stability. Further, an additional advantage of the present cleaning formulation is that it confers lubricity to an interface between the surface being cleaned and the wiper, chamber or the like which is moved across the surface.